Antibiotic-resistant gonorrhea, a diarrhea-causing superbug and a class of fast-growing killer bacteria dubbed a "nightmare" were classified as urgent public-health threats in the United States on Monday.

According to a new report by the U.S. Centers for Disease Control and Prevention (CDC), at least 2 million people in the United States develop serious bacterial infections that are resistant to one or more types of antibiotics each year, and at least 23,000 die from the infections.

"For organism after organism, we're seeing this steady increase in resistance rates," Dr Thomas Frieden, director of the CDC, said in a telephone interview. "We don't have new drugs about to come out of the pipeline. If and when we get new drugs, unless we do a better job of protecting them, we'll lose those, also."

Overprescribing of antibiotics is a chief cause of antibiotic resistance, affording pathogens the opportunity to outwit the drugs used to treat them. Only a handful of new antibiotics have been developed and brought to market in the past few decades, and only a few companies are working on drugs to replace them.

In addition to resistant gonorrhea, the others now seen as urgent threats, according to the first-of-its-kind report released on Monday, are C. difficile and the killer class known as carbapenem-resistant Enterobacteriaceae, or CRE.

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The report was conceived to bring together as much information as possible about drug-resistant superbugs and how to slow their spread, with a hope of preserving the remaining drugs that still work, Frieden said.

The United States is not alone in raising the alarm over antibiotic drug resistance. Last March the chief medical officer for England said antibiotic resistance poses a "catastrophic health threat". That followed a report last year from the World Health Organization that found a "superbug" strain of gonorrhea had spread to several European countries.

The CDC report ranks the threat of drug-resistant superbugs into three categories - urgent, severe and concerning - based on factors such as their health and economic impacts, the total number of cases, the ease with which they are transmitted and the availability of effective antibiotics.

Among the top three threats deemed "urgent" is CRE, which Frieden last March called a "nightmare bacteria" because even the strongest antibiotics are not effective against it.

According to the report, CRE accounts for 9,300 healthcare-associated infections. The two most common types of CRE - carbapenem-resistant Klebsiella spp. and carbapenem-resistant E. coli - account for some 600 deaths each year.

"For CRE, we're seeing increases from 1 state to 38 states in the last decade," Frieden said.

HOSPITAL THREAT

C. difficile, the most common hospital-based infection in the United States, made the list of urgent threats both because it has begun to resist antibiotics and because it preys on the overuse of antibiotics.

C. difficile, which causes life-threatening diarrhea, spreads from person to person on contaminated equipment and on the hands of healthcare workers and visitors. It is especially stubborn in hospitals because of the widespread use of antibiotics, which kill protective bacteria in the gut for months, allowing invaders such as C. difficile to flourish.

According to the report, C. difficile causes 250,000 infections and kills 14,000 people in the United States each year, adding $1 billion annually in excess medical costs. Deaths from C. difficile rose 400 percent from 2000 to 2007 due to the emergence of a drug-resistant strain of the bacteria.

The third "urgent" threat in the report is drug-resistant Neisseria gonorrhea, which causes 246,000 U.S. cases of the sexually transmitted disease gonorrhea each year. Gonorrhea is increasingly becoming resistant to tetracycline, cefixime, ceftriaxone and azithromycin - formerly the most successful treatments for the disease.

Gonorrhea is especially troublesome because it is easily spread, and infections are easily missed. In the United States, there are approximately 300,000 reported cases, but because infected people often have no symptoms the CDC estimates the actual number of cases is closer to 820,000.

If left untreated, gonorrhea can lead to pelvic inflammatory disease, ectopic pregnancy, stillbirths, severe eye infections in babies and infertility in men and women.

"The three organisms that have been chosen as urgent are all increasing at an alarming rate to which therapies are limited," said Dr Edward Septimus, an infectious disease expert at HCA Healthcare System in Houston, Texas, and a member of the Infectious Diseases Society of America's Antimicrobial Resistance Workgroup.

Septimus, who was not involved with the CDC report, said the pathogens in the urgent and serious categories - which include Methicillin-resistant Staphylococcus aureus, or MRSA, and drug-resistant tuberculosis - are "certainly worthy of immediate response. I do believe it's a looming public-health crisis," he said.

In addition to ranking the threat of superbugs, the report outlines a four-point plan to help fight the spread of antibiotic resistance.

Not surprisingly, it underscores the need for new antibiotics, citing ever-slowing development efforts by pharmaceutical companies due to the high cost of such programs and relatively low profit margins of the drugs.

It also stresses the need for hospitals to prevent infections from occurring and to contain the spread of resistant infections; carefully tracking the spread of resistant bacteria; and ensuring that antibiotics are prescribed only to patients who need them.

"It's not too late," Frieden said. "There are things we can do that can stop the spread of drug resistance. We need to scale up the implementation of those strategies."